Research And Design Of Automatic Calibration System For High-precision Bell Gas Flow Standard Device

The gas flow standard device is a kind of system that formed by hardware and software in order to reappearing the gas flow standard value. It can transfer the accurate and uniform gas flow value to the flow meter used for natural gas trade measurement. The establishment of this device has an important significance to guarantee the accuracy, reliability and fairness of natural gas trade measurement. The bell prover gas calibration facility of National Oil and Gas Large Flow Rate Measurement Station is one of the primary standards of domestic gas flow standard device. Before reformation equipment of the automatic calibration system is old with single function, and has not been able to satisfy the need of accurate measurement and transmission of the value. Through the reformation to the automatic calibration system, the uncertainty of the bell prover gas calibration facility can be ensure and the system functions are enhanced. And can meet the needs of value transmission of gas flow meter for the Northeast region and even the whole country.In this paper, the measurement process as well as data acquisition and control system has been redesigned and reformed based on the original bell standard measuring vessel. The calibrating function to critical flow Venturi nozzle has been added. And the uncertainty of system is ensure. The reliability and calibrating efficiency of system has been improved by the design of the software and hardware system.In this paper, the influence factors about the metering accuracy of the bell prover gas calibration facility have been analyzed, and the steps are adopted to solve corresponding questions. By the high accuracy sensor and controller, the accuracy and representativeness of sampling data has been improved and the uncertainty level of the system is ensure. In order to improve the calibration efficiency and reliability, the security programs such as the interlock protection program, the redundancy design program of displacement measurement, and the quick adjustment memory program of the flow have been designed. By adding the measurement process, the calibrating function to critical flow Venturi nozzle has been realized.After the completion of the reform, the uncertainty of the system was re-evaluated, and the repeatability tests, stability tests have been taken on the facility. And using seven sets of high accuracy and stability roots flowmeter imported from German ELSTER as comparison standard, the comparison has been carried out among the calibration result of this device and the German original factory calibration K-factor and the Shanghai Institute of measurement calibration K-factor. The test results show that the repeatability and the stability of the facility can meet the requirements and have fairly high accuracy of calibration.By this reform the low-pressure natural gas value system of our country has been improved. It has an important significance to ensure the accuracy and unity of natural gas trade measurement for the Northeast region and even the whole country.